Computer and network security is an area of considerable concern. While there is great interest in being able to remotely monitor resources such as industrial facilities across computer networks, lack of security of those monitored resources has required the development of specialized devices that provide defenses against security threats to computers, networks, and other devices in the monitored resources that go beyond the protection of firewalls and other traditional Internet security software and hardware systems. For high security resources, such as those used by government agencies and some commercial facilities, such as computer-controlled industrial facilities, energy, or water utilities, conventional firewall and other security systems may not provide reliable enough protection from undesired intrusions.
Today, we consider one single, high-value asset to be critical because to lose it would cause widespread disruption (for example: a power plant), but in aggregate, thousands of pieces of commercial equipment represent a similar threat and the number of attack vectors is exponentially higher. Widespread cyberattack of commercial or “subcritical” equipment, from building chillers to sewage pumps, would cause economic disruption and compromise public safety. For example, attacks on the air handlers in a region's hospital network, the refrigeration equipment at pharmacies and grocery stores, or the chilled water pumps serving Virginia's data centers could have severe impact.
For these types of resources, one-way data transfer may be a critical requirement to isolate the protected network from intrusion by malware or other malicious actors outside the protected network. While conventional Internet firewalls and software systems such as specially configured operating system may be designed to restrict data transfer to unidirectional data flow, software-based one-way data transfer systems are difficult to validate and verify, and may be subject to intentional or inadvertent misconfiguration that may allow data leakage or intrusions in the reverse direction.
Malicious attacks to date have focused largely on data theft or network disruption, but attacks on physical assets are becoming more frequent. Attackers can compromise IoT devices and, for example, (a) Recruit devices into botnets used for distributed denial of service (DDOS) attacks; (b) Open a back door into a corporate network; or (c) Change operating behavior of the device, leading to device failure or safety concerns.
Data diode devices have been developed to provide hardware-enforced one-way data transfer, using techniques as simple as severing the receive pin in an RS-232 cable to more complex techniques involving the use of optical cables or opto-isolator components that transfer electrical signals between two isolated circuits with light. An opto-isolator (also called an optocoupler) uses a optical emitter such as an LED that generates light responsive to electrical signals, while an optical sensor such as a phototransistor receives the light and converts the light into electrical signals. Because there is electrical isolation between the two sides of the opto-isolator, this physically enforces one-way communication across the opto-isolator.
However, because common Internet protocols depend upon two-way communication, a data diode requires additional components beyond an opto-isolator (or a simple serial cable with the receive line interrupted) to allow effective one-way communication.
Traditional data diodes are used to protect critical infrastructure, such as nuclear reactors or oil refineries by broadcasting equipment status in a one-way manner. These traditional data diodes are expensive and have required customization by skilled implementation teams.